Biomass torrefaction: Modeling of reaction thermochemistry

Based on the evolution of volatile and solid products predicted by a previous model for willow torrefaction (Bates and Ghoniem, 2012) a thermochemical model has been developed to describe their thermal, chemical, and physical properties as well as the rates of heat release. The first stage of torrefaction, associated with hemicellulose decomposition, is exothermic releasing between 40 and 280 kJ/kginitial. The second stage is associated with the decomposition of the remaining lignocellulosic components, completes over a longer period, and is predicted to be either endothermic or exothermic depending on the temperature and assumed solid properties. Cumulative heat release increases with the degree of torrefaction quantified by the mass loss. The rate of mass loss and rate of heat release increase with higher temperatures. The higher heating value of volatiles produced during torrefaction was estimated to be between 4.4 and 16 MJ/kg increasing with the level of mass loss.BP (Firm

3D Eulerian modeling of thin rectangular gas-solid fluidized beds: Estimation of the specularity coefficient and its effects on bubbling dynamics and circulation times

This study aims at investigating the influence of the wall boundary conditions and specifically the specularity coefficient on the fluidization behavior of a thin rectangular fluidized bed by means of 3D numerical simulation employing an Eulerian description of the gas and the solid phases. Thin rectangular fluidized beds have been extensively used in the research literature since it is assumed that the flow behaves like a simpler two-dimensional flow and hence they offer validation data for 2D simulations. However, the effects of the front and the back walls are significant, influencing the sensitivity of the fluidization hydrodynamics to the third dimension whose consideration is thus necessary. In order to investigate the influence of the specularity coefficient, ϕ (a parameter controlling the momentum transfer from the particles to the wall), on the fluidization hydrodynamics, a parametric analysis is conducted and the response of the bubble dynamics, reflecting the gasmotion, and the circulation fluxes, displaying the solids motion, are examined in detail. The computational results are compared with available experimental data in order to determine the values of ϕ that lead to the accurate description of the fluidization hydrodynamics via a two-fold validation strategy which involves the calculation of the circulation time and the solids concentration maps. It is observed that the appropriate value of the specularity coefficient depends rather strongly on the superficial gas velocity of the bed.BP (Firm

Modeling of Biomass Char Gasification, Combustion, and Attrition Kinetics in Fluidized Beds

Char conversion is one of the most pivotal factors governing the effectiveness of fluidized bed gasification systems. Gasification-assisted attrition is a phenomenon whereby heterogeneous reactions progressively weaken a char’s structure throughout its lifetime leading to enhanced attrition and the production of a significant fraction of fines that exit the reactor unconverted. While this effect has been observed and measured experimentally, few models have been developed to quantitatively account for it, particularly for biomass chars. In this study, a transient gasification and combustion particle model is presented to describe primary fragmentation, attrition, and heterogeneous reactions of a single batch of particles. A conversion-dependent structural function is proposed to describe gasification-assisted attrition, and the model parameters are fitted to published experimental data from Ammendola, P.; Chirone, R.; Ruoppolo, G.; Scala, F. Proc. Combust. Inst. 2013, 34 (2), 2735–2740. The fragile structure of char derived from wood chips contributes to a higher initial attrition rate than char from wood pellets, but the hardness of both feedstocks is shown to deteriorate rapidly as they convert. A shrinking particle combustion model which accounts for variable feedstock properties is comprehensively presented and validated against the aforementioned data set. The combustion behaviors of both feedstocks are found to strongly depend on particle size/geometry because of significant mass transfer limitations. Using a residence time distribution approach, the model is extended to describe a continuously fed system in order to examine the sensitivity of steady-state outputs (conversion and residence time) to the operating temperature, pressure, and kinetics. As the temperature increases, the char reactivity also increases but the coupled and competing effect of gasification-assisted attrition acts to shorten the residence time of the char particles making complete char conversion very difficult even at 900 °C—the upper operating temperature limit for most single-stage fluidized bed gasification systems. Low operating temperatures result in longer average residence times and higher steady-state char inventories, and slower kinetics lowers the overall conversion. Because of inhibition effects, elevated operating pressures have a smaller impact on improving conversion compared to higher temperature. The steady model further provides a rigorous method for estimating the maximum stable biomass feeding rates as a function of relevant independent parameters including reactor temperature, pressure, volume, and feedstock characteristics.BP (Firm)United States. Department of Energy (National Energy Technology Laboratory Research Participation Program

Addressing Cervical Cancer in Central Appalachia

Rural women, particularly those residing in Appalachia, have some of the nation’s highest cervical cancer mortality rates. With support from federal and private grants, the University of Kentucky Center for Excellence in Rural Health-Hazard is attempting to address this issue. Eastern Kentucky-based researchers are surveying 18- to 26-year-old female community health center patients and college students about their risk factors for the disease, and then offering them free Gardasil, a vaccine against the virus that causes most cervical cancer cases

Are Killer Bees Good for Coffee? The Contribution of a Paper\u27s Title and Other Factors to Its Future Citations

How can the title of a paper affect its subsequent number of citations? We compared the citation rate of 5941 papers published in the journal Biological Conservation from 1968 to 2012 in relation to: paper length; title length; number of authors; paper age; presence of punctuation (colons, commas or question marks); geographic and taxonomic breadth; the word ‘method’; and the type of manuscript (article, review). The total number of citations increased in more recently published papers and thus we corrected citation rate (average number of citations per year since publication) by publication age. As expected, review papers had, on average, twice the number of citations compared to other types of articles. Papers with the greatest geographic or taxonomic breadth were cited up to twice as frequently as narrowly focused papers. Titles phrased as questions, shorter titles, and papers with more authors had slightly higher numbers of citations. However, overall, we found that the included parameters explained only 12% of the variability in citation rate. This suggests that finding a good title is necessary, but that other factors are more important to construct a well-cited paper. We suggest that to become highly cited, a primary requirement is that papers need to advance the science significantly and be useful to readers

Western Juniper Field Guide: Asking the Right Questions to Select Appropriate Management Actions

Strong evidence indicates that western juniper has significantly expanded its range since the late 1800s by encroaching into landscapes once dominated by shrubs and herbaceous vegetation (fig. 1). Woodland expansion affects soil resources, plant community structure and composition, water, nutrient and fire cycles, forage production, wildlife habitat, and biodiversity. Goals of juniper management include an attempt to restore ecosystem function and a more balanced plant community that includes shrubs, grasses, and forbs, and to increase ecosystem resilience to disturbances. Developing a management strategy can be a difficult task due to uncertainty about how vegetation, soils, hydrologic function, and wildlife will respond to treatments. When developing a management strategy, the first and possibly most important step towards success is asking the right questions. Identifying the attributes of the area to be treated and selecting the right treatments to be applied are of utmost importance. One must ask questions addressing the kind of site (that is, potential natural vegetation, soils, etc.), the current state of the site (that is, successional, hydrologic, etc.), what components need to be restored, how the management unit fits in with the overall landscape mosaic, and the long-term goals and objectives for the area or region. Keep in mind sagebrush-steppe vegetation is dynamic and management strategies must take into account multi-decade time frames. This guide provides a set of tools that will help field biologists, land managers, and private landowners conduct rapid qualitative field assessments that address the kind of site and its current state. These tools include a list of questions to be addressed and a series of photographs, keys, tables, and figures to help evaluate a site. Conducting this assessment will help prioritize sites to be treated, select the best treatment, and predict outcomes. Success of a juniper management program may be greatly enhanced if an interdisciplinary team of local managers and resource specialists, who are experienced with vegetation, fuels, soils, hydrology, wildlife, and economic and sociological aspects of the local resource, use this guide to aid their decision-making

Three lessons conservation science can learn from the COVID-19 pandemic: A call to action from ECRs.

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Effects of several types of biomass fuels on the yield, nanostructure and reactivity of soot from fast pyrolysis at high temperatures

peer-reviewedThis study presents the effect of biomass origin on the yield, nanostructure and reactivity of soot. Soot was produced from wood and herbaceous biomass pyrolysis at high heating rates and at temperatures of 1250 and 1400° C in a drop tube furnace. The structure of solid residues was characterized by electron microscopy techniques, X-ray diffraction and N2 adsorption. The reactivity of soot was investigated by thermogravimetric analysis. Results showed that soot generated at 1400° C was more reactive than soot generated at 1250° C for all biomass types. Pinewood, beechwood and wheat straw soot demonstrated differences in alkali content, particle size and nanostructure. Potassium was incorporated in the soot matrix and significantly influenced soot reactivity. Pinewood soot particles produced at 1250° C had a broader particle size range (27.2–263 nm) compared to beechwood soot (33.2–102 nm) and wheat straw soot (11.5–165.3 nm), and contained mainly multi-core structures

Low-volatility compounds contribute significantly to isoprene secondary organic aerosol (SOA) under high-NO_x conditions

Recent advances in our knowledge of the gas-phase oxidation of isoprene, the impact of chamber walls on secondary organic aerosol (SOA) mass yields, and aerosol measurement analysis techniques warrant reevaluating SOA yields from isoprene. In particular, SOA from isoprene oxidation under high-NOx conditions forms via two major pathways: (1) low-volatility nitrates and dinitrates (LV pathway) and (2) hydroxymethyl-methyl-α-lactone (HMML) reaction on a surface or the condensed phase of particles to form 2-methyl glyceric acid and its oligomers (2MGA pathway). These SOA production pathways respond differently to reaction conditions. Past chamber experiments generated SOA with varying contributions from these two unique pathways, leading to results that are difficult to interpret. This study examines the SOA yields from these two pathways independently, which improves the interpretation of previous results and provides further understanding of the relevance of chamber SOA yields to the atmosphere and regional or global modeling. Results suggest that low-volatility nitrates and dinitrates produce significantly more aerosol than previously thought; the experimentally measured SOA mass yield from the LV pathway is ∼0.15. Sufficient seed surface area at the start of the reaction is needed to limit the effects of vapor wall losses of low-volatility compounds and accurately measure the complete SOA mass yield. Under dry conditions, substantial amounts of SOA are formed from HMML ring-opening reactions with inorganic ions and HMML organic oligomerization processes. However, the lactone organic oligomerization reactions are suppressed under more atmospherically relevant humidity levels, where hydration of the lactone is more competitive. This limits the SOA formation potential from the 2MGA pathway to HMML ring-opening reactions with water or inorganic ions under typical atmospheric conditions. The isoprene SOA mass yield from the LV pathway measured in this work is significantly higher than previous studies have reported, suggesting that low-volatility compounds such as organic nitrates and dinitrates may contribute to isoprene SOA under high-NOx conditions significantly more than previously thought and thus deserve continued study

Measurement error in a multi-level analysis of air pollution and health: a simulation study.

BACKGROUND: Spatio-temporal models are increasingly being used to predict exposure to ambient outdoor air pollution at high spatial resolution for inclusion in epidemiological analyses of air pollution and health. Measurement error in these predictions can nevertheless have impacts on health effect estimation. Using statistical simulation we aim to investigate the effects of such error within a multi-level model analysis of long and short-term pollutant exposure and health. METHODS: Our study was based on a theoretical sample of 1000 geographical sites within Greater London. Simulations of "true" site-specific daily mean and 5-year mean NO2 and PM10 concentrations, incorporating both temporal variation and spatial covariance, were informed by an analysis of daily measurements over the period 2009-2013 from fixed location urban background monitors in the London area. In the context of a multi-level single-pollutant Poisson regression analysis of mortality, we investigated scenarios in which we specified: the Pearson correlation between modelled and "true" data and the ratio of their variances (model versus "true") and assumed these parameters were the same spatially and temporally. RESULTS: In general, health effect estimates associated with both long and short-term exposure were biased towards the null with the level of bias increasing to over 60% as the correlation coefficient decreased from 0.9 to 0.5 and the variance ratio increased from 0.5 to 2. However, for a combination of high correlation (0.9) and small variance ratio (0.5) non-trivial bias (> 25%) away from the null was observed. Standard errors of health effect estimates, though unaffected by changes in the correlation coefficient, appeared to be attenuated for variance ratios > 1 but inflated for variance ratios < 1. CONCLUSION: While our findings suggest that in most cases modelling errors result in attenuation of the effect estimate towards the null, in some situations a non-trivial bias away from the null may occur. The magnitude and direction of bias appears to depend on the relationship between modelled and "true" data in terms of their correlation and the ratio of their variances. These factors should be taken into account when assessing the validity of modelled air pollution predictions for use in complex epidemiological models